Finding A Function From A Power Series

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Homework Help Overview

The discussion revolves around finding the sum of a power series and determining its radius of convergence, specifically the series \(\sum_{n=1}^{\infty} (-1)^{n+1}\frac{(x-1)^n}{n}\). Participants are exploring the relationship between the series and its derivative.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the radius of convergence and express uncertainty about finding the sum of the series. There are attempts to relate the series to its derivative, with questions about recognizing the type of series formed.

Discussion Status

Some participants have confirmed the form of the derivative of the function associated with the series. There is ongoing exploration of whether the resulting series can be classified as a geometric series, with prompts for further reasoning and clarification.

Contextual Notes

There is a hint provided regarding the derivative of the series, and participants are encouraged to consider the implications of their findings without reaching a definitive conclusion.

Bashyboy
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Homework Statement


Find the sum of the series and its radius of convergence:

[itex]\sum_{n=1}^{\infty} (-1)^{n+1}\frac{(x-1)^n}{n}[/itex]


Homework Equations





The Attempt at a Solution


I found the radius of convergence, but I wasn't sure how to find the sum of the power series.
 
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Bashyboy said:

Homework Statement


Find the sum of the series and its radius of convergence:

[itex]\sum_{n=1}^{\infty} (-1)^{n+1}\frac{(x-1)^n}{n}[/itex]


Homework Equations





The Attempt at a Solution


I found the radius of convergence, but I wasn't sure how to find the sum of the power series.

Hint: If you call that series f(x), what is f'(x)?
 
Would it be [itex]f'(x) = \sum_{n=0}^{\infty} (-1)^{n+1}(x-1)^{n-1}[/itex]?
 
Bashyboy said:
Would it be [itex]f'(x) = \sum_{n=0}^{\infty} (-1)^{n+1}(x-1)^{n-1}[/itex]?

Yes. And do you recognize what kind of series that is?
 
If you distribute the (-1)^(n+1) to the (x-1)^(n-1) would it be a geometric series?
 
Bashyboy said:
Would it be [itex]f'(x) = \sum_{n=0}^{\infty} (-1)^{n+1}(x-1)^{n-1}[/itex]?

Bashyboy said:
If you distribute the (-1)^(n+1) to the (x-1)^(n-1) would it be a geometric series?

Do you really have to ask? What do you think? Why? Show us what you would do if it is.
 

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